The incorporation of electronic devices with pneumatic tire structures yields many practical advantages. Tire electronics may include sensors and other components for relaying tire identification parameters and also for obtaining information regarding various physical parameters of a tire, such as temperature, pressure, tread wear, number of tire revolutions, vehicle speed, etc. Such performance information may become useful in tire monitoring and warning systems, and may even potentially be employed with feed back systems to regulate proper tire parameters and vehicle performance.
Yet another potential capability offered by electronics systems integrated with tire structures corresponds to asset tracking and performance characterization for commercial vehicular applications. Commercial truck fleets, aviation craft and earth mover/mining vehicles are all viable industries that could utilize the benefits of tire electronic systems and related information transmission. Radio frequency identification (RFID) tags can be utilized to provide unique identification for a given tire, enabling tracking abilities for a tire. Tire sensors can determine the distance each tire in a vehicle has traveled and thus aid in maintenance planning for such commercial systems. Vehicle location and performance can be optimized for more expensive applications such as those concerning earth-mining equipment.
One particular type of condition-responsive device that has been utilized to determine various parameters related to a tire or wheel assembly is an acoustic wave device, such as a surface acoustic wave device (SAW). Such SAW devices include at least one resonator element made up of interdigital electrodes deposited on a piezoelectric substrate. When an electrical input signal is applied to a SAW device, selected electrodes cause the SAW to act as a transducer, thus converting the input signal to a mechanical wave in the substrate. Other electrodes then reverse the transducer process and generate an electrical output signal. A change in the output signal from a SAW device, such as a change in frequency, phase and/or amplitude of the output signal, corresponds to changing characteristics in the propagation path of the SAW device. In some SAW device embodiments, monitored resonant frequency and any changes thereto provide sufficient information to determine parameters such as temperature, pressure, and strain to which a SAW device is subjected.
Acoustic wave devices in the tire industry have typically been implemented as passive devices, as it has often been challenging in the past to implement complex electronic assemblies within a tire structure. Such passive acoustic wave devices are not provided with their own power supply. Instead, passive acoustic wave devices are interrogated by remote transceiver devices which transmit an energizing signal from a remote location to the acoustic wave device. The acoustic wave device stores some of this transmitted energy during excitation and may then transmit output signals indicating the resonant frequencies at which each resonator element in the acoustic wave device is excited.
Providing signals from a remote transceiver to an acoustic wave device often requires complex integrated circuitry as the interrogator must include electronics for both transmitting a signal to the acoustic wave device as well as for receiving a signal therefrom. Interrogation by a remote receiver often results in high levels of electromagnetic emissions as the transmitted signal must typically be characterized by power levels high enough to propagate through the communication channel formed by the tire or wheel assembly before reaching and energizing the acoustic wave device. Such high levels of electromagnetic emissions characterize a relatively inefficient means to interrogate the SAW transducer and may provide a potential source of interference in other nearby wireless communication systems. Thus, it may be desirable to provide an alternative system for relaying data between such tire electronics assemblies and a remote receiver location.
Another concern associated with passively operating acoustic wave devices is that many such devices typically exist in the same energizing field. This situation could occur when one sensor is provided in each of four or more tires on a given vehicle. When a remote transceiver emits an energizing signal to interrogate a given acoustic wave device, a plurality of signals may be received from multiple acoustic wave devices. A fundamental problem lies in the ability to distinguish among the received signals. For instance, since a shift in frequency output of an acoustic wave device is often being used to measure a physical phenomenon such as temperature or pressure, when several such acoustic wave devices are in the same energizing field at the same time conflicts such as overlaps in the respective resonant frequencies of the acoustic wave devices may exist, preventing resolution of unique frequency shifts for each respective acoustic wave device.
One known method for addressing the problem of utilizing multiple acoustic wave devices in the same energizing field corresponds to adding phase shift reflectors around planar antennas associated with the acoustic wave devices. This technique utilizes addressing functionality to overcome the problem of identification of various transmitting acoustic wave devices, but may limit other aspects of acoustic wave operation and is fundamentally limited by the number of available addresses. Thus, it may be desirable to provide an alternative solution for utilizing multiple acoustic wave devices in the same energizing field.
While various implementations of acoustic wave devices such as SAW sensors in tire electronic systems have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.
It should be appreciated that although examples of sensors have been described above with regard to potential application in a tire or wheel environment, the improved electronic assemblies and related aspects of the present invention as hereafter described can be utilized in any application in which it is desired to remotely sense physical parameters such as temperature or pressure. Examples of such application environments include, without limitation, tire or wheel assemblies or other locations associated with a vehicle, oil wells, refineries, water plants, etc.